1. Field of the Invention
This invention relates to a novel family of crystalline aluminosilicates, to a method for preparation thereof and to use thereof in catalytic conversion of hydrocarbons.
2. Description of the Prior Art
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various type of hydrocarbon conversions. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels. These cavities and channels are precisely uniform in size. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline aluminosilicates. These aluminosilicates can be described as a rigid three-dimensional framework of SiO.sub.4 and A1O.sub.4 in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total aluminum and silicon atoms to oxygen is 1:2. The electrovalence of the tetrahedra containing aluminum is balanced by the inclusion in the crystal of a cation, for example, an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of aluminum to the number of various cations, such as Ca/2, Sr/2, Na, K or Li is equal to unity. One type of cation may be exchanged either entirely or partially by another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given aluminosilicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic aluminosilicates. These aluminosilicates have come to be designated by letter or other convenient symbols, as illustrated by zeolite A (U.S. Pat. No. 2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat. No. 3,130,007), zeolite ZK-5 (U.S. Pat. No. 3,247,195), zeolite ZK-4 (U.S. Pat. No. 3,314,752) and zeolite ZSM-5 (U.S. Pat. No. 3,702,886), merely to name a few.
One such crystalline aluminosilicate, a rare natural zeolite, is ferrierite. Ferrierite has been described by Graham (Roy, Soc. Canada, Proc. and Trans., 3rd Ser., 12, 185-190) and by Staples (Am. Mineral. 40, 1095-99). The formula of the natural mineral ferrierite is given as (Na, K).sub.4 Mg.sub.2 (Si.sub.30 Al.sub.6) O.sub.72 (OH).sub.2 .18 H.sub.2 O. Barrer and Marshall (Am. Mineral. 50,484-85) in 1965 reexamined the X-ray powder diffraction pattern of a strontium zeolite Sr-D, synthesized by Barrer and Marshall in 1964 (J. Chem. Soc., 485-89) and concluded that it was closely related to natural ferrierite. A synthetic sodium form was briefly described by Senderov (Geokhimiya 9, 820-29) and a Ca-Na form of ferrierite produced by Coombs, Ellis, Fyfe and Taylor (Geochem. Cosmochin. Acta 17, 53-107) was not identified as such.